On 3/19/07, David Schwartz <[EMAIL PROTECTED]> wrote:
> I didn't suggest adding any unfairness! I suggested being fair by > user/job/process instead of being fair by thread (which is actually > unfair as it favors multi threaded processes over single threaded > processes). Wouldn't that be unfair because it favors multi-user approaches over single-user approaches with the same number of processes?
Not necessarily. Use GID rotations too. And if you can't assign these properly, it's your own/your distro's fault.
Consider two otherwise equivalent web server designs. They both use a helper process owned by the user who owns the file the web server is sending. One does a lot of work in the helper process, the other does very little. A "fair by user" scheduler would give the approach that puts more work in the helper process more CPU than the one that puts little work in the helper process.
Indeed, it's a drawback. Though a configurable one.
Being fair by user builds lots of assumptions into the scheduler. When they're not true, the scheduler becomes sub-optimal. For example, consider a web server that runs two very important tools, 'foo' and 'bar'. Rather than running them as root, they run as users 'foo' and 'bar' for security. "Fair to user" would mean that just because most other people are using 'foo', I get less CPU when I try to use 'foo', because the OS doesn't know the "real user", just the fake user who owns the process -- a security decision that has no relationship to fairness. This would be handled perfectly by a "fair to process" approach.
Then, use a group quota. But checking that will be slower, and that overhead might kill other gains.
As for favoring multi-threaded processes over single-threaded processes, sometimes that's what you want.
Not on desktop. Typical multi-threaded workloads: - apache - some P2P clients - some audio servers/applications (small number of threads) Single-threaded is much more popular.
Consider two servers,
^ ^ ^ Well, aren't we discussing desktops? Server admins can fine-tune the rights and CPU quotas per group.
one using thread per job the other using process per job. Does it make sense to give the "process per job" server as much CPU to do a single task as the "thread per job" server gets for all the clients it's dealing with?
Not necessarily. You see, the processes themselves are schedulable, the threads aren't.
It's really more important that the scheduler be tunable and predictable.
This kind of scheduler, yes. Except it's much more tunable than a simple fair or unfair scheduler, and much more suited to real-time applications.
That way, we can tell it what we want and get it. But the scheduler cannot read our minds.
That's why the per-user or per-group part would have to be optional. It just doesn't make much sense on single-user desktops. Then, RSDL design or even RSDL+bonus could be used. The bonus part would have to be really simple, e.g. priority inheritance for pipes, startup priority boost for nice 0 tasks. (warning - fork bombs. :P ) No sleep estimator. Maybe these would suffice? The interactive bonus would be disabled by default, same as per-user/per-group scheduling. Some syscalls would have to be added, maybe using LSM framework? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/